Data communication is the process by which two or more data terminals or peripherals send information to each other. In its simplest form, a data communication system, or network, is comprised of a transmitter, a transmission path, and a receiver.
Networks are classified according to different characteristics. One such characteristic is its size. A local area networks (LAN) typically connects devices within a building or a school campus while a wide-area network (WAN) interconnects devices within one city or between different cities.
Network topologies in data communication are greatly diversified. The topology refers to a map, or physical location, of the cables linking the devices in the network. Network topologies typically fall into one of the following types: bus, ring, star or mesh network. The ring topology connects all nodes by a serial connection while a star network connects each device to a central hub. Each of the topologies has advantages and disadvantages depending on its application.
Finally, the method of transferring data within the network is a very important characteristic. The communication options include choosing parallel or serial transmission, synchronous or asynchronous transmission, and single or multiple signal transmission capabilities.
The hardware and software rules and procedures, called protocol, dictate how and when data is transferred. Most networks utilize serial asynchronous transmission protocols. Asynchronous transfer, used in most LANs, uses continuous bursts of fixed-length packets, or cells, to transmit data. But because the transfer is not synchronous, signal information indicating the start and stop point of the signal must be included with the substantive data being sent. As a result, asynchronous transfer loses transmission efficiency by having to send procedural data.
While many systems utilize serial asynchronous transmission, they differ on the protocol used in the system. A protocol is a set of rules that determines how and when the users get to send information across the network. Protocol options include Ethernet carrier sense multiple access/collision detection (CSMA/CD), token-passing, or multiplexing. Token-passing protocol only allows one device, the one with the token, to transmit on the network at any one time. Conversely, the ethernet carrier sense multiple access/collision detection (CSMA/CD) protocol is essentially a random access, first in time rule. The first device to transmit on the network without encountering a collision wins the right to finish its transmission. When a collision does occur, both devices to cease transmission, reset, and wait a random period of time before retransmitting. Lastly, multiplexing spaces out the time or wavelength of the transmission between all the inputs, so they each take turns sending information.
A typical network communication involves computers and peripherals connected in a LAN by a mesh or ring topology. Different LAN systems are then connected in a larger network, like a WAN, using a ring topology. Often, the internetwork link is called a backbone, a very high data-rate link.
While Ethernet protocol and hardware is ubiquitous for LAN systems, it has not been a viable option for WAN operation. The ethernet collision detection protocol limited the overall length of the network. For a data packet to successfully transmit on ethernet protocol, the time for the packet to transmit with no collision detection being returned to the sender is theoretically equivalent to the round trip of the furthest path in the network. For a WAN, this distance can be very high. Using ethernet collision detection protocol on a WAN would increase the frequency of collisions, and increase the response time to a point where the system may be perpetually incapacitated. Hence, a need existed for a different protocol that would successfully transmit an ethernet packet on ethernet hardware over a long distance while assuring equity to transmit on the network. In this way, communications between LANs could be seamless, efficient, reliable, and cost-effective.
As networks become larger and devices transfer more data, a need arises for the links between networks to operate at a very high transmission rate with an associated high-speed protocol. Also, because of the high-cost of the physical layer of a network, a need exists for expansion technology to utilize existing equipment and interfaces while allowing increases in operating performance. As such, it would be prohibitively expensive to tear out existing ring topology WAN networks and replace them with a new type of topology.
In an effort to meet increased bandwidth transmission demands, fiber optic systems have been favored for many backbone connections in a WAN network due to their greater traffic-carrying capacity. In response, the industry developed a standard for fiber optic communication called synchronized Optical Network (SONET) to allow transmission systems to be interoperable. With transmission rates in the order of gigabits per second, the prior art has the capability of meeting the high transmission-rate needs. However, the prior art has many limitations that detract from its usefulness.
SONET requires the use of SONET protocol for transmission over the fiber optic link. Thus, all LAN data must be translated twice. For example, if data is to be sent from LAN `X` to LAN `Y` over a SONET link, then the LAN frame configuration protocol (i.e. ethernet) must be translated into the SONET frame configuration at the data enters the SONET Link. Likewise, the SONET frame configuration must be translated to the LAN frame configuration when data leaves SONET and enters the LAN. This step requires complex and computationally-intensive translations. The translations incur extra costs, overhead, and latencies when ethernet packets running over LANs are converted to frames in a SONET or an equivalent protocol. Consequently, the conversion/reconversion of data frames from one protocol to another is computationally expensive, time-consuming, and inefficient.
Furthermore, the SONET frame is inflexible. It cannot be modified to a specific network link or network protocol. Thus even if the network connection is point-to-point, SONET still requires source and destination addresses in the frame overhead. Hence, the overhead can be redundant and wasteful. Furthermore, the circuit-switch based modulation/demodulation is an unnecessary complication for packet switching. Thus a need exists for a network communication to communicate with LAN's without timely and complex translations and without redundant overhead.
Another limitation of the prior art is its high cost. As its name implies, SONET requires the use of fiber optic cable. SONET does not have the flexibility to operate on different types of a physical layer. Hence, if a user has a metal cable network (i.e., on a WAN) and wants to use the SONET standard, the system must undergo a costly transformation from cable to fiber optics. In light of this limitation, a need exists for a high transmission rate network that has the flexibility to run on either a cable physical layer with its standard equipment or on the more costly fiber optic physical layer.
The prior art protocol uses time division multiplexing to divide the transmission resources between multiple nodes. A guaranteed minimum bandwidth for each ensures access to the network. Similarly, a preassigned maximum bandwidth from each node prevents overloading the network. Unfortunately, this protocol does not take advantage of local traffic conditions between nodes in a WAN. Thus, for example, one node may need to transmit data at a rate equal to the capability of the system to an adjacent node. However, even if that data is the only traffic on that local link, the preassigned maximum bandwidth will limit the transmission to less than the system capability. Hence, the full capability of the system is not fully utilized because of the inflexible preassigned maximum bandwidth for each node. Consequently, a need exists for a flexible protocol that has the flexibility to regulate data transmission on a local and an overall scale that allows the system to be used to its fullest potential.
Finally, the prior art has no method for guaranteeing fairness among the different sources of data. Hence, one node might have better access to the network and be able to send more data than an adjacent node. Fairness becomes an issue when the demands for transmitting data exceed the system's capability. At that point, a node or device must be controlled as to how and when it accesses the transmission network. For ethernet collision detection protocol and for token passing, the ability to transmit on the network is determined by randomness. There is no protocol or algorithm for dividing the limited resources of the network to ensure each user or node gets an equal chance of transmitting or receiving their data on the network.
Prior Art FIGS. 1A, 1B, and 1C, present a logical illustration of various alternative network protocols in the prior art is presented. A communication network 105, such as a WAN or MAN, has Nodes 1, node 2, node 3, and node 4 are communicatively coupled by communication links 106. Tributary communication links 107 connect each node to another communication network, such as a LAN. Information is transmitted on the network in the form of data packets. The packet typically contains administrative data, such as the sender and receiver address and error-control information, and substantive data. The protocol of the network dictates the length and specific contents of the packet. For any sizable amount of information, more than one data packet will be required to send the entire batch of information. Hence a device may want to transmit a series of data packets, called a packet stream, on the network from one node to another.
Prior Art FIG. 1A represents a full-speed network access protocol. Communication network 105 uses a full-speed protocol that allows any node to transmit a data packet on the network in a direction 118 along the network. The protocol is representative of ethernet. Any packet from any node can try to transmit at one-hundred percent from any node at any time the network is not in use. When the network is not busy, or when just one node wants to transmit, this process works without collisions. However, when the network becomes busy, i.e. when many nodes want to transmit, then collisions on the communication network will occur as indicated. The values of "1" by communication link 107 indicates that the node wants to transmit its data at 100% of the network's capacity. When node 2, 3, and 4 all want to transmit at 100% capacity, a collision will occur, and the system will not be able to transmit data from any node. Hence, when collisions occur, the system becomes bogged down is unreliable and inefficient. The net result is wasted time, unused network resources, and repeated attempts to resend data.
Referring now to Prior Art FIG. 1B, an equal right network access protocol is presented. In this protocol, upstream nodes always half the available transmission resources available to them. As a result, a downstream node will have a disproportionately large share of the network's transmission resources. Conversely, the upstream nodes will eventually approach zero transmission rate. For example, in FIG. 1B, node 2 has a 1/2 transmission rate (i.e. 50% of the network's transmission capability) while node 3 has a 1/4th (25%) transmission rate and node 4 has a 1/8th (about 12%) transmission rate. Overall, the communication network's resources are distributed in a very nonlinear fashion (i.e. 50%, 25%, 12%, etc.). Furthermore, the network capacity is not fully utilized (i.e. 50%+25%+12%=87%). Hence, quality of service suffers severely for users on upstream nodes as they have to wait longer for access to the network. As a result, the communication network performance has low utility to the users and can result in significant wait times and inefficient transmission of data
Referring now to Prior Art FIG. 1C, an upstream first network access protocol is presented. In this protocol, upstream nodes have the first chance to use the full resources of the network. Again, this is unfair because an upstream node can utilize the full capacity of the network without sharing with downstream nodes. Thus, node 4 has a 1 (or 100%) transmission rate on the network. Quality of service to users on downstream nodes suffers in this method as well.
Overall, Prior Art FIGS. 1A, 1B, and 1C illustrate the prior art attempts to solve the problem of distributing limited communication network resources. However, these solutions have significant limitations and do not work effectively. The prior art solutions do not provide fair access of the network's transmission resources to the different nodes. Rather, an uneven or biased transmission rate exists for the nodes trying to transmit in the network. Therefore, a need exists for a protocol and algorithm to regulate traffic flow in a fair manner to improve quality of service and reliability.
In summary, a need exists for a network system and a method for transmission on the network that has a high transmission-rate at a low cost. Still another need exists for a transmission protocol and architecture that does not require complex and computationally-intensive translation from the existing LAN protocols. A further need exists for a network transmission protocol and architecture that has flexibility to adjust its transmission capabilities to high and low data traffic conditions between networks and between local nodes. Yet another need exists for a network transmission protocol that has the flexibility to operate on different types of physical layer such as fiber or cable. Lastly, there is a need for a protocol to regulate traffic in a manner that ensures fairness in the amount of data transmitted on the network. The present invention provides a solution that satisfies all these needs.